The presumptive Democratic nominee Hillary Clinton holds a small 5-point lead over Republican challenger Donald Trump, according to the June CNBC All-American Survey, with a large chunk of the voting public remaining undecided.

The poll of 801 registered voters conducted June 11-14 shows Clinton with a 40 percent to 35 percent lead, but the poll's margin of error is plus or minus 3.5 percentage points. Pollsters for CNBC say the survey shows a tight race with 25 percent undecided, including 14 percent who right now choose "neither" candidate.

"It's the hallmark of a campaign with high negatives around these candidates," said pollster Micah Roberts with Public Opinion Strategies. The poll was conducted by POS from the Republican side and Hart Research Associates from the Democratic side.

But both pollsters pointed to one group that could increase Clinton's margin. The survey shows that 20 percent of voters who had supported Democrat Bernie Sanders currently choosing neither candidate. "I've seen nothing to suggest that Sanders supporters won't break in favor of Clinton,'' said Jay Campbell, Hart Research's senior vice president. He points out that Sanders supporters who have made their decisions back Clinton about 6 to 1.

In other findings:

Americans are divided on which candidate is best for the economy, 39 percent to 38 percent in favor of Clinton. They are also tied on who is best for dealing with terrorism, and who is best for a person's personal financial situation and for small business.

Clinton holds leads on who is best for health care, trade, immigration and the lower and middle classes.

Trump leads on who would be best for stocks, regulating Wall Street and banks, dealing with the budget deficit, large companies and the wealthy.

Fifty-eight percent say a Trump presidency would make America's standing in the world worse, compared with 38 percent for Clinton.

The horrific attack in Orlando, Florida, occurred in the middle of the survey but pollsters said they found little effect on presidential choice. The economy and unemployment ranked as the top election issue for Americans both before and after the massacre, chosen by 26 percent of Americans compared with 20 percent who chose foreign policy, world leadership and combating terrorism. But the foreign policy category did rise by 6 points from 15 percent to 21 percent after the attack.

The effect on presidential choice, however, appeared to be minimal, and Roberts, the Republican pollster, suggested that could spell trouble for Trump. After the attack, CNBC asked which candidate has the best policies for "dealing with terrorism and homeland security." The 408 respondents to that question (half the sample, with a margin of error of 4.8 points) gave Trump only a slight edge of 40 percent to 38 percent. Roberts said that going back to 2002, Republican candidates typically hold 10 to 36 point leads over Democrats on national security issues.

"That's a major red flag for Trump," said Democratic pollster Campbell.

Among the challenges facing Clinton, while she is seen as best for the middle class by a 43 percent to 32 percent margin, the actual middle class is less sure. Among those with incomes from $50,000 to $75,000 and among blue collar workers, Clinton and Trump are tied on the middle-class question.

Clinton also faces a large block of Sanders voters choosing neither. She'll have to bring them on board, and has just a 3-point lead among independents, 35 percent of whom choose neither candidate.

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